Prior to treatment, patients will be randomized to receive either AeroVanc twice daily (bid), or placebo bid. Patients will be stratified based on the presence of a Pseudomonas aeruginosa (P. aeruginosa) co-infection that is being treated with a chronic suppression regimen. Patients with P. aeruginosa co-infection can be on any chronic inhaled suppression regimen (or nothing if the patient is considered stable in the opinion of the investigator despite the lack of treatment). Regardless of treatment regimen, if there is an off month, screening should be scheduled so that AeroVanc or placebo administration can be given during this time. Patients with no off month should be screened so that the AeroVanc or placebo administration period coincides with a treatment cycle other than TOBI (e.g., Cayston or colistin). All patients must have at least a 24-hour washout period after stopping their anti-Pseudomonas therapy and prior to the Visit 2 (Baseline) pre-dose microbiology sputum sample. The AeroVanc or placebo treatment duration is 28 days, during which efficacy and safety parameters will be measured, and after which patients will be followed up for 56 days.